Four new tris(ethylenediamine)-chelated metal complexes [Zn(en)₃]I₂·0.5en (1), [Cd(en)₃]Cl₂·H₂O (2), [Cd(en)₃]Br₂ (3), and [Hg(en)₃]Cl₂ (4) have been synthesized by solvothermal reactions. The complexes contain discrete [M(en)₃]²⁺ (M = Zn, Cd, Hg) cations and halide anions. The Zn²⁺ and Cd²⁺ ions are six-coordinated by three ethylenediamine molecules to form octahedra, while the Hg²⁺ ion has a trigonal prism coordination geometry. These complexes all display fluorescent properties in the blue range, which are attributed to a ligand-to-metal charge-transfer mechanism according to molecular orbital calculations. The solid-state diffuse reflectance spectra show that 1–4 are wide band-gap semiconductors. IR and thermogravimetric analyses for 1–4 are also presented in this paper.